1. Field of the Invention
The present invention relates to a harmonic wave generator, and more particularly, to a harmonic wave generator using a non-linear material.
2. Description of the Related Art
It is possible to exchange energy among electromagnetic fields having different frequencies. One type of apparatus to which this phenomenon is applied is a harmonic generator. A second harmonic generating (SHG) apparatus which doubles the frequency of light using a non-linear material is the most representative.
An electrical dipole oscillates harmonically and an harmonically when the amplitude of light from the outside is large enough. From the analysis of the frequency component of the light wave, it is noticed that a light wave includes several kinds of harmonic waves as well as a fundamental wave. In general, if the crystal structure of a non-linear material has inverted symmetrical characteristics, the potentials of charges are symmetrical to one another. Thus, the lowest non-linear polarization in which dipoles are combined is a third harmonic. A second harmonic component of non-linearly polarized light exists in a non-linear material having no inverted symmetrical characteristics. Also, a process of emitting light by a polarization oscillating with a double frequency is called a second harmonic generation.
As the high density of optical recording media and high precision of laser printers increase, a light source having a short wavelength and high power is increasingly required. Laser diodes to emit light of a blue wavelength, which is a conventional short wavelength, have been developed at a high price. Thus, it is now difficult to commonly use the laser diodes in the reproduction of the optical recording media and the laser printers.
Light having a short wavelength and high power may be obtained from an SHG apparatus. However, a conventional half-wavelength generator, which can reduce the wavelength of light by half using the SHG apparatus includes a solid laser which emits light having a wavelength of 1064 nm or 946 nm as a light source. Light emitted from the solid laser as described above is converted into light having half the original wavelength, i.e., a wavelength of 546 nm or 473 nm, by a material to generate a second harmonic wave.
Accordingly, the conventional half-wavelength generator is high-priced and has many optical parts. Thus, the conventional half-wavelength generator is bulky and is not easy to assemble. As a result, the conventional half-wavelength generator is not suitable to reproduce data from optical recording media of high density and devices requiring small-sized lasers having high power.